Achlys was a pseudo-primordial goddess, and the daughter of Nyx. She was responsible for dropping the 'mist of death' upon those before they were taken away finally by Thanatos, the Greek god of peaceful death.

The mist of death was the incoming darkness of a person closing their eyes for the final time, which caused the Greeks to entitle her as 'The Eternal Night." She was believed to have existed before Chaos/Khaos, and was even described in one instance in the shield of Heracles by the poet Hesoid. His description read:

'She was "dismal and dejected, green and pale, dirty-dry, fallen in on herself with hunger, knee-swollen, and the nails were grown long on her hands, and from her nostrils the drip kept running, and off her cheeks the blood dribbled to the ground, and she stood there, grinning forever, and the dust that had gathered and lay in heaps on her shoulders was muddy with tears."'References: https://mrpsmythopedia.wikispaces.com/Achlys